This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from an application for Method For Setting Read Bias Current of Magneto-Resistive Head earlier filed in the Korean Industrial Property Office on Jan. 15, 1998 and there duly assigned Ser. No. 49735/1998.
The present invention relates to a hard disk driving method, and more particularly, to a method for setting a read bias current to the optimal bias current in order to read data written on a hard disk using a magneto-resistive (MR) head.
In a conventional inductive head, coils are wound around a head core and magnetic flux changes in a disk induces a voltage across the bead coil. In the inductive head, inductance of the head coil should be down as a frequency of a data signal becomes high, in order to stabilize the data signal. When the inductance of the head coil becomes high, the induced voltage of the head is decreased, thereby making it unstable to detect the data signal.
An MR head by which the problem may be solved includes an MR sensor for easily detecting changes in magnetic flux to stably detect even a high-frequency data signal. Unlike the conventional inductive head in which the magnetic flux changes induces the voltage by the head coil, the MR sensor detects the changes in the magnetic flux as changes in resistance while reading of data, and the conventional inductive head structure is adopted while writing of data, so that a signal-to-noise (S/N) ratio may be improved.
In order to operate a hard disk in the optimal condition, various parameters relating to the hard disk should be maintained at the optimum state. Among those parameters, a read bias current which is the current applied to a head to read data written on the hard disk should be optimized such that the head can read data without error. In particular, the MR head has a recording density higher than in a coil type head. Thus, if the read bias current is optimized, the MR head can be read more data without error than the coil head. In order to set the read bias current using the MR head, first the MR head moves onto tracks without any defects and then data is written to the tracks. After writing data, the MR head applies a stress to the tracks, and the data is read from the tracks to thereby determine the current causing the lowest error rate as the read bias current.
However, in the aforementioned method, the optimum value of the read bias current is determined depending on the erroneous state. Thus, multiple reading processes are required, thereby consuming much time.
U.S. Pat. No. 5,790,334 to Cunningham for a Circuit and Method For Optimizing Bias Supply in a Magnetoresistive Head Based on the Thermal Properties of the MR Head Itself discloses a testing circuit and method for optimizing the read bias current in an MR head which includes the steps of varying the bias current applied to the head. However, Cunningham uses a complicated circuit to accomplish the task. In addition, the frequency components of the read data are not analyzed in Cunningham to determine the optimum read bias current.
To solve the above problem, it is an object of the present invention to provide a method for setting a read bias current, which is for reading data written to a hard disk with the optimal bias current using a magneto-resistive (MR) head.
It is further an object to provide a method for determining the optimum read bias current for an MR head that requires little or no circuitry.
It is still yet another object of the present invention to determine the optimum read bias current by analyzing the frequency spectrum of read data.
Accordingly, to achieve the above first object, there is provided a method for setting a read bias current for reading data written to a hard disk using a magneto-resistive (MR) head, the method comprising the steps of: (a) writing data to the hard disk in a predetermined frequency; (b) reading data from the disk while varying a bias current value applied to the MR head; (copyright) analyzing frequency characteristics of the data read in the step (b); and (d) selecting the bias current at which the read data has the best frequency characteristics, as the bias current of the MR head.